1. Technical Field
The present invention relates to a technique of taking statistics of communication data flowing through a network.
2. Description of the Related Art
As the Internet is widely used as the essential social infrastructure, in addition to the conventional best-effort type data communication, there is communication of various data, such as audio data, animation data, and transaction data of mission-critical tasks, that require the assurance of high communication quality. With widespread use of the ADSL (Asymmetric Digital Subscriber Line) technique and FTTH (Fiber To The Home) technique, access lines for broadband are generally used to increase the communication traffic.
In such circumstances, telecommunication carriers and Internet service providers require the technique of taking statistics of communication data flowing through a network, in order to assess the status of communication in the network. There is especially a high demand for the technique of taking statistics of communication data in each flow, which is classified by, for example, the source and the destination of communication data, the application used, and the quality level.
One proposed technique of taking statistics of communication data for each flow is a cache flow statistical technique disclosed in Japanese Patent Laid-Open No. 2006-5402. This proposed technique obtains a preset combination of identifiers (for example, a source address, a destination address, a source port number, and a destination port number) from header information of each received packet and counts up the number of packets having identical values of the respective identifiers in the preset combination, so as to sum up the communication traffic for each flow.
One proposed technique of collecting statistical information on a high-speed line is disclosed in Japanese Patent Laid-Open No. 2006-352831. This proposed technique accumulates information to be updated up to a preset number and collectively performs reading data from a memory, updating statistical information, and writing data into the memory, thus enhancing the speed of statistical operation.
The cache flow statistical technique disclosed in the former cited reference analyzes header information on reception of every packet. This technique advantageously has the extremely high capability of flow analysis. The technique, however, requires analyses of the header information for all the received packages and storage of the results of analyses into a memory. With increase of line speed to 40 Gbps or further to 100 Gbps, the access rate to the memory makes it difficult to record the required statistical information into the memory.
The speed-up technique of the statistical operation disclosed in the latter cited reference accumulates the statistical information in the buffer for the purpose of collective update. The statistical operation of diverse flows, however, has the following problems. For example, in application of a relatively low-capacity buffer, even a small number of flows fully occupy the capacity of the buffer, so that only a little amount of information is accumulated in the buffer. There is accordingly little speed-up effect by accumulation of information. The speed-up technique of the statistical operation gives only the overhead reduction effect of the statistical updating.